1. Field of the Invention
This invention relates to apparatus for variably attenuating a light beam, such as a laser beam, via the selective polarization thereof.
2. Description of the Prior Art
In U.S. Pat. No. 4,398,806 issued to K. E. Bennett, there is disclosed an optical attenuator for variably attenuating a light beam (e.g. a laser beam) via the phenomenon of polarization. Such an attenuator comprises a pair of transparent, wedge-shaped plates of homogeneous dielectric material (e.g. glass or fused silica) positioned in the optical path to transmit and polarize an incident light beam as a function of the angle of incidence. The plates are arranged so that their respective angles of convergence are in opposite directions, and so that a major surface of one plate is parallel to a major surface of the other. Means are provided for simultaneously rotating the plates to vary the angle of incidence of the light beam on the first plate and to assure that the beam emerging from the second plate is parallel to the incoming beam. Optionally, a second pair of wedge-shaped plates, similarly structured, arranged and rotatably driven, is provided to receive the beam transmitted by the first pair and to refract the beam so that such beam, as transmitted by the second pair is colinear with the beam as incident on the first pair.
In optical attenuators of the above type, it is necessary for many applications that each of the four refractive elements be constructed from high quality optical media which can transmit electromagnetic radiation at a desired wavelength (that of the beam being attenuated) within the 0.3-10 micron spectral region. Also, each element must be accurately shaped to achieve the desired colinearity between input and output beams. These requirements, of course, add significant cost to such attenuators and, to some extent, limit their utility.